1. Technical Field
This disclosure relates to processes for producing cumene More specifically, this disclosure relates to the recovery of polyalkylated benzene byproducts from the alkylation of benzene with propylene to form cumene, namely diisopropylbenzene (DIPB) triisopropylbenzene (TIPB), which can then be transalkylated back to cumene.
2. Description of the Related Art
The alkylation of aromatics with olefins to produce monoalkyl aromatics is a well developed art which is practiced commercially in large industrial units. One commercial application of this process is the alkylation of benzene with propylene to form cumene (isopropylbenzene) which is subsequently used in the production of phenol and acetone Those skilled in the art are therefore familiar with the general design and operation of such alkylation processes
The performances of alkylation processes for producing monoalkyl aromatics such as cumene are influenced by the stability and activity of the solid catalyst at the operating conditions of the process. For example, as the molar ratio of aromatic (benzene) per olefin (propylene) increases, current catalysts typically exhibit an improved selectivity to the monoalkyl aromatic—cumene. But even at these high molar ratios of benzene per propylene, polyalkylbenzene by-products such as diisopropylbenzene (DIPB) and triisopropylbenzene (TIPB) will accompany cumene production.
Although the formation of DIPB and TIPB might be viewed as by-products that represent a reduction in the efficient use of the propylene, both DIPB and TIPB can be readily transalkylated with the benzene using a transalkylation catalyst to produce the more valuable cumene product. So-called combination processes combine a first alkylation process that produces primarily cumene but which also produces DIPB and small amounts of TIPB with a second transalkylation process that converts the DIPB and TIPB back to cumene in order to the maximize cumene production. Upstream of the second transalkylation, the DIPB and TIPB must be separated from the other heavy alkylation and transalkylation by-products such as diphenylalkanes, which are collectively referred to herein as “heavies.”
The separation or recovery of DIPB and TIPB is performed in a “polyalkylate” column. Because currently utilized cumene operating conditions and catalyst systems produce mainly DIPB as byproduct, with very little TIPB, TIPB has not been economically worth recovering and the polyalkylate columns of cumene production areas are designed to recover DIPB, not TIPB. However, newer catalyst systems produce increased amounts of TIPB at optimum reaction conditions. As a result, there is a need for a process that efficiently recovers TIPB as well as DIPB.
However, there is a problem associated with the removal of TIPB from the heavies Current polyalkylate columns operate under vacuum at a top pressure of approximately 3 psia and at a bottom pressure of approximately 8-10 psia The most economical way to reboil at the bottom of the column is to use high-pressure steam. High-pressure steam is typically available at 600 psig and at 485° F. Unfortunately, current polyalkylate columns produce significant TIPB yield losses in the heavies stream or bottoms product.
Therefore, design changes to polyalkylate columns are needed to maintain or increase DIPB recovery and to significantly increase TIPB recovery. TIPB this can be accomplished, cumene yield can be increased using current transalkylation techniques